The present invention is related to methods for joining bulk solidifying amorphous alloys with non-amorphous metals.
Bulk solidifying amorphous alloys are a family of amorphous alloys which can be cooled from the molten state at substantially lower cooling rates, about 500 K/sec or less, than older conventional amorphous alloys and still substantially retain their amorphous atomic structure. As such, they may be produced in amorphous form and with thicknesses of 1 millimeter or more, significantly thicker than possible with the older amorphous alloys that require much higher cooling rates. Bulk-solidifying amorphous alloys have been described, for example, in U.S. Pat. Nos. 5,288,344; 5,368,659; 5,618,359; and 5,735,975, the disclosures of which are incorporated by reference.
A family of bulk-solidifying alloys of most interest may be described by the molecular equation: (Zr,Ti)a(Ni,Cu,Fe)b(Be,Al,Si,B)c, where a is in the range of from about 30 to about 75, b is in the range of from about 5 to about 60, and c is in the range of from 0 to about 50, in atomic percentages. These alloys can accommodate substantial amounts of other transition metals, up to about 20 atomic percent, and preferably metals such as Nb, Cr, V, and Co. A preferred alloy family is (Zr,Ti)d(Ni,Cu)e(Be)f, where d is in the range of from about 40 to about 75, e is in the range of from about 5 to about 60, and f is in the range of from about 5 to about 50, in atomic percentages. Still a more preferably composition is Zr41Ti14Ni10Cu12.5 Be22.5, in atomic percentages. Bulk solidifying amorphous alloys are desireable because they can sustain strains up to about 1.5 percent or more without any permanent deformation or breakage; they have high fracture toughness of about 10 ksi sqrt(in) or more (sqrt denotes square root), and preferably 20 ksi sqrt(in) or more; and they have high hardness values of 4 GPa or more, and preferably 5.5 GPa or more. In addition to desirable mechanical properties, bulk solidifying amorphous alloys also have very good corrosion resistance.
Because the properties of the bulk solidifying amorphous alloys may not be needed for some parts of the structure, and because they are relatively expensive compared to non-amorphous materials, such as aluminum alloys, magnesium alloys, steels, and titanium alloys many cases, bulk solidifying amorphous alloys are typically not used to produce an entire structure. It is therefore necessary to join is the bulk solidifying amorphous alloy portion of the structure to the portion of the structure that is the non-amorphous solidifying alloy.
A number of different joining methods have been explored including: mechanical fasteners, which may be used in some cases, but they have disadvantages in both mechanical properties and physical properties, such as corrosion resistance, when in contact with the bulk solidifying amorphous alloy; adhesives, which may be used, but only if the service temperature is sufficiently low that the adhesive retains its strength; and finally, brazing and welding, which are possibilities, but satisfactory techniques and materials have not been developed for the brazing and welding of amorphous materials.
Accordingly, a need exists for a method of joining amorphous materials to non-amorphous materials in an inexpensive, but robust manner.
The present invention is directed to a method of joining a bulk-solidifying amorphous material to a non-amorphous material including, forming a cast mechanical joint between the bulk solidifying amorphous alloy and the non-amorphous material.
In a first embodiment, the joint is formed by controlling the melting point of the non-amorphous and bulk-solidifying amorphous alloys (amorphous metals). In one such embodiment, where the non-amorphous metal has a higher melting point than the melting point of the amorphous metal, the non-amorphous metal is properly shaped and the bulk-solidifying amorphous alloy is melted and cast against the piece of preformed non-amorphous metal by a technique such as injection or die casting. In another such embodiment, where the non-amorphous metal has a lower melting point than the melting point of the amorphous metal, the non-amorphous material may be joined to the bulk-solidifying amorphous alloy by melting the non-amorphous alloy and casting it, as by injection or die casting, against a piece of the properly shaped and configured bulk-solidifying amorphous alloy which remains solid.
In a second embodiment, the joint is formed by controlling the cooling rate of the non-amorphous and amorphous metals. In one such embodiment, a non-amorphous metal is cast against a piece of pre-formed bulk-solidifying amorphous alloy, and cooled from the casting temperature of the non-amorphous alloy down to below the glass transition temperature of bulk-solidifying amorphous alloy at rates at least about the critical cooling rate of bulk solidifying amorphous alloy.
In either of the above embodiments, a system, such as a heat sink may be provided to ensure that the temperature of either the pre-formed amorphous metal or pre-formed non-amorphous metal always stay below the glass transition temperature of the bulk-solidifying amorphous alloy.
In still another embodiment, the shapes of the pieces of the bulk-solidifying amorphous alloy and the non-amorphous metal are selected to produce mechanical interlocking of the final pieces.